Process and apparatus for communicating with a user antenna

ABSTRACT

A process for cooperative aerial inter-antenna beamforming for communication between (a) multiple moving platforms, each platform having an aerial antenna mounted thereon, such that the aerial antennas have variable positions and orientations over time, and (b) at least one antenna mounted on user equipment having a lower altitude than the aerial antennas; the process involving transmitting data relating to the positions and orientations of the aerial antennas to a processing system, the processing system calculating and transmitting beamforming instructions to the aerial antennas, the aerial antennas thereby transmitting or receiving respective component signals for each user antenna, the component signals for each user antenna having essentially the same information content but differing in their phase and usually amplitude, so as to form a cooperative beam from the cooperative sum of the signals between the aerial antennas and the user antenna. A method of determining the position of a moving aerial antenna or antenna element mounted on at least one moving platform, such that the aerial antennas have variable positions and orientations over time, the method involving determining the phase difference yi, being a fraction of a wavelength between the values 0 and 1, between signals of known wavelength λi; transmitted between (a) i ground based transmitters which may be backhaul base stations, wherein i is at least three, the ground based transmitters having known position to within λi/10 and (b) the aerial antenna or antenna element, thereby establishing the distance from the base station to the aerial antenna or antenna element to be λi(ni+yi), wherein ni is an unknown integer; determining the position of the aerial antennas or antenna elements approximately by differential GPS or other methods to within a small number of wavelengths λi thereby establishing that ni can be one of a limited number of possible integer values for each signal; the number of base stations and their positions being sufficient to allow elimination of the possible values of ni that are inconsistent with the limited number of possible values for ni from the other ground based transmitters, until only one integer value for each ni is established; establishing the location of the aerial antenna or antenna element by triangulation of its known distance λi(ni+yi), from at least three ground based transmitters.

TECHNICAL FIELD

The invention relates to aerial inter-antenna beamforming utilizingmultiple phased-array antennas, which enables the delivery ofinformation services, including telecommunications, earth observation,astronomical and positioning services. It also enables multipleconventional antennas to be used in a similar manner.

BACKGROUND TO THE INVENTION

High altitude platforms (aircraft and lighter than air structuressituated from 10 to 35 km altitude)—HAPS, have been proposed to supporta wide variety of applications. Areas of growing interest are fortelecommunications, positioning, observation and other informationservices, and specifically the provision of high speed Internet, e-mail,telephony, televisual services, games, video on demand, mapping servicesand global positioning.

High altitude platforms possess several advantages over satellites as aresult of operating much closer to the earth's surface, at typicallyaround 20 km altitude. Geostationary satellites are situated at around40,000 km altitude, and low earth orbit satellites are usually at around600 km to 3000 km altitude. Satellites exist at lower altitudes buttheir lifetime is very limited with consequent economic impact.

The relative nearness of high altitude platforms compared to satellitesresults in a much shorter time for signals to be transmitted from asource and for a reply to be received (which has an impact on the“latency” of the system). Moreover, high altitude platforms are withinthe transmission range for standard mobile phones for signal power andsignal latency. Any satellite is out of range for a normal terrestrialmobile phone network, operating without especially large or specialistantennas.

High altitude platforms also avoid the rocket propelled launches neededfor satellites, with their high acceleration and vibration, as well ashigh launch failure rates with their attendant impact on satellite cost.

Payloads on high altitude platforms can be recovered easily and atmodest cost compared to satellite payloads. Shorter development timesand lower costs result from less demanding testing requirements.

U.S. Pat. No. 7,046,934 discloses a high altitude balloon for deliveringinformation services in conjunction with a satellite.

US 20040118969 A1, WO 2005084156 A2, U.S. Pat. No. 5,518,205 A, US2014/0252156 A1, disclose particular designs of high altitude aircraft.

However, there are numerous and significant technical challenges toproviding reliable information services from high altitude platforms.Reliability, coverage and data capacity per unit ground area arecritical performance criteria for mobile phone, device communicationsystems, earth observation and positioning services.

Government regulators usually define the frequencies and bandwidth foruse by systems transmitting electromagnetic radiation. The shorter thewavelength, the greater the data rates possible for a given fractionalbandwidth, but the greater the attenuation through obstructions such asrain or walls, and the more limited diffraction which can be used toprovide good coverage. These constraints result in the choice of carrierfrequencies of between 0.7 and 5 GHz in most parts of the world withtypically a 10 to 200 MHz bandwidth.

There is a demand for high data rates per unit ground area, which israpidly increasing from the current levels of the order 1-10 Mbps/squarekilometre.

To provide high data rates per unit ground area, high altitude unmannedlong endurance (HALE) aircraft, or free-flying or tethered aerostats,would need to carry large antenna(s) to distinguish between closelybased transceivers on the ground. A larger diameter antenna leads to asmaller angular resolution of the system, hence the shorter the distanceon the ground that the system can resolve. Ultimately the resolution isdetermined by the “Rayleigh criterion” well known to those skilled inthe art. The greater the antenna resolution, the higher the potentialdata rates per unit ground area are.

However fitting extremely large diameter antenna or antennas of 50metres or more onto platforms is not feasible with current or envisagedplatform technology.

Phased array digital “beamforming” (DBF) and multi beam horn (MBH)antennas have been considered for high altitude platforms in forexample, R. Miura and M. Suzuki, “Preliminary Flight Test Program onTelecom and Broadcasting Using High Altitude Platform Stations,”Wireless Pers. Commun., An Int'l. J., Kluwer Academic Publishers, vol.24, no. 2, January 2003, pp. 341-61. Other references include:http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=620534,http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=933305,http://digital-library.theiet.org/content/journals/10.1049/ecej_20010304,http://digital-library.theiet.org/content/journals/10.1049/el_20001316http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=4275149&pageNumber%3D129861However, the prior art suggests that use of high altitude platforms doesnot represent a promising way forward to delivering next generation highrate communication means.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a process for cooperativeaerial inter-antenna beamforming for communication between (a) multiplemoving platforms, each platform having an aerial antenna mountedthereon, such that one or more aerial antennas have variable positionsand orientations over time, and (b) at least one antenna mounted on userequipment, UE, having a lower altitude than the aerial antennas; theprocess involving transmitting data relating to the positions andorientations of the aerial antennas to a processing system, theprocessing system calculating and transmitting beamforming instructionsto the aerial antennas, the aerial antennas thereby transmitting orreceiving respective component signals for each user antenna to enablecommunication with at least one user antenna, the component signalsreceived or transmitted from the aerial antennas for each user antennahaving essentially the same information content but differing in theirphase and usually amplitude, so as to form a cooperative beam from thecooperative sum of the signals between the aerial antennas and the userantenna.

Additionally, the invention relates to a process for cooperative aerialinter-antenna beamforming for communication between at least two aerialantennas, mounted on at least one moving platform, such that one or moreof the aerial antennas have variable positions and orientations overtime, and at least one antenna mounted on user equipment having a loweraltitude than the aerial antennas; the process involving transmittingdata relating to the positions and orientations of the aerial antennasto a data processing system, a processing system calculating andtransmitting beamforming instructions to the aerial antennas, the aerialantennas thereby transmitting or receiving respective component signalsfor each user antenna, the component signals for each user antennahaving essentially the same information content but differing in theirphase and amplitude, so as to form a cooperative beam from thecooperative sum of the signals between the aerial antennas and the userantenna, the resulting cooperative beam thereby having the same orsimilar properties of a beam formed from a notional single aerialantenna large enough to encompass the positions of the at least twoaerial antennas.

By the term “same or similar” is meant properties such as beam size.

In a second aspect, the invention relates to apparatus for providing acommunication network, for communication between (a) multiple movingplatforms, each platform having an aerial antenna mounted thereon, suchthat one or more aerial antennas have variable positions andorientations over time, and (b) at least one user antenna mounted onuser equipment having a lower altitude than the aerial antennas; thenetwork involving a data processing system adapted to receive datarelating to the positions and orientations of the aerial antennas, theprocessing system being further adapted to generate and transmitbeamforming instructions to the aerial antennas, the aerial antennasbeing adapted to generate or receive respective component signals foreach user antenna, the component signals for each user antenna havingessentially the same information content but differing in their phaseand amplitude, so as to form a cooperative beam between the cooperativesum of the signals between the aerial antennas and the user antenna, theresulting cooperative beam thereby having the same or similar propertiesof a beam formed from a notional single aerial antenna large enough toencompass the positions of the at least two aerial antennas.

Additionally, the invention relates to apparatus for providing acommunication network, for communication between at least two aerialantennas, mounted on at least one moving platform, such that one or moreaerial antennas have variable positions and orientations over time, andat least one user antenna mounted on user equipment having a loweraltitude than the aerial antennas; the network involving a dataprocessing system adapted to receive data relating to the positions andorientations of the aerial antennas, the processing system being furtheradapted to generate and transmit beamforming instructions to the aerialantennas, the aerial antennas being adapted to generate or receiverespective component signals for each user antenna, the componentsignals for each user antenna having essentially the same informationcontent but differing in their phase and amplitude, so as to form acooperative beam between the cooperative sum of the signals between theaerial antennas and the user antenna, the resulting cooperative beamthereby having the same or similar properties of a beam formed from anotional single aerial antenna large enough to encompass the positionsof the at least two aerial antennas.

Synthetic aperture synthesis has long been known in radio astronomywhere the resolution of a large antenna is synthesized by using thesignals from appropriately spaced relatively small antennas. IndeedMartin Ryle and Antony Hewish shared the Nobel prize for physics in 1974for this and other contributions to the development and use of radiointerferometry. Related technology to aperture synthesis has been usedfor many years in low frequency radio communication to submarines, inacoustics, phased arrays in LTE and WiFi systems. However its use forcommunication between a plurality of aerial antennas, one or more ofwhich are moving, and user equipment, has never been previouslyconsidered.

Thus, according to the invention, if the positions and orientations ofthe aerial antennas are known sufficiently well, processing to generatethe component signals can be carried out to produce a synthesizedcooperative beam which is much narrower than that which could beachieved by any one of the individual aerial antennas.

Thus, through application of aperture synthesis principles a cooperativebeam can be formed that has a narrow width as could be provided by anotional single aerial antenna large enough to encompass the positionsof the at least two aerial antennas. As would be known to a personskilled in the art, the larger the notional antenna, the narrower thebeam.

Building on techniques developed for the quite remote technical field ofradio astronomy it has been discovered that generation of these verynarrow cooperative beams can be achieved by altering the phasing andweighting of the various signals sent to or received from each aerialantenna.

The advantages of such a narrow cooperative beam are numerous and thevarious details and advantages of the invention will be discussed below.

As will be appreciated, it is a preferred feature of the invention tohave accurate positional and orientation information of the aerialantennas. These may be moving with varying ground and/or air speedsleading to displacements that are significant in the context ofbeamforming as will be discussed below.

The invention exploits the ability of suitable positioning systems todetermine the relative position of the antennas, on multiple platforms,to within a fraction of a wavelength of the electromagnetic radiationbeing used, even up to GHz frequencies. As described above, withappropriate signal processing to enable “aperture synthesis,” similar tothat commonly used in radio astronomy, it is then possible to obtain abeam resolution comparable to that of an elevated antenna with adiameter equal to the maximum separation distance of the aerialantennas.

A significant advantage of having a very narrow cooperative beam is thatother user equipment nearby, say within a few metres or less, can alsoreceive or transmit a full bandwidth signal—on the same or similarcarrier frequency if desired. This would therefore significantlyincrease the capacity of the system to provide data bandwidth to aplurality of users.

In order to carry out the process of the invention, an aerial antenna'sposition relative to all the other aerial antennas should be determinedto within approximately ⅙ of a wavelength, preferably 1/10 of awavelength, and this has become possible with modern positioningtechniques to the accuracy required for the operation of aerial antennasfor mobile communications.

Knowledge of the physical location of all the aerial antennas, and ifthey are phased arrays, the elements within the aerial antennas isessential for the generation and production of useful beams. Thelocation of these aerial antennas or antenna elements needs to bedetermined to within a fraction of a wavelength, preferably to less thana 10^(th) of a wavelength, which is ˜1.5 cm for a 2 GHz carrier signal.At this precision there is little signal loss or beam shape distortionespecially when considering that multiple platforms are likely to haverandomized positional errors.

The determination of the platform position can be performed at theground by measuring the phase of the platform signals at multiple groundstations and triangulating the position of the platform. With suitablemeasurement of platform orientation and deformation, the position andorientation of each antenna element can be determined.

More elegantly, the position of the antenna elements can be found byreversing the beamforming process and by correlating signals fromantennas on the array, if the antenna position is known to moderateaccuracy by differential GNSS, e.g. GPS, GLONAS, GALILEO or othermethods. In this manner, the position “solution” can be found by usingsignals from multiple ground stations or beacons that are in positionsknown to less than a 10^(th) of a wavelength. This then gives a veryaccurate location and orientation of the platform.

In a third aspect, the invention relates to a method of determining theposition of a moving aerial antenna or antenna element mounted on atleast one moving platform, such that the aerial antennas have variablepositions and orientations over time, the method involving determiningthe phase difference y_(i), being a fraction of a wavelength between thevalues 0 and 1, between signals of known wavelength λ_(i) transmittedfrom or to i ground based transmitters which may be backhaul basestations, wherein i is at least three, the ground based transmittershaving a known position to within λ_(i)/10, and the aerial antenna orantenna element, thereby establishing the distance from the base stationto the aerial antenna or antenna element to be λ_(i)(n_(i)+y_(i)),wherein n_(i) is an unknown integer; determining the position of theaerial antennas or antenna elements approximately by differential GlobalPositioning System, GPS, or other methods to within a small number ofwavelengths λ_(i) thereby establishing that n_(i) can be one of alimited number of possible integer values for each signal; the number ofbase stations and their positions being sufficient to allow eliminationof the possible values of n_(i) that are inconsistent with the limitednumber of possible values for n_(i) from the other ground basedtransmitters, until only one integer value for each n_(i) isestablished; establishing the location of the aerial antenna or antennaelement by triangulation of its known distance λ_(i)(n_(i)+y_(i)), fromat least three ground based transmitters.

Thus the invention relates to a method of determining the positions ofat least two antennas at an elevated location, at least one that ismoving, such that the aerial antennas have variable positions andorientations over time, the method involving two stages, the first beingto determine by external reference, typically using differential GNSS,e.g., GPS, the position of the platform, and therefore the antenna,within the limits of the accuracy achievable, typically less than 20 cm,more typically less than 10 cm. This is comparable to a wavelength attypical mobile phone frequencies of several GHz.

The second stage is then to detect the signals from each of multipleground stations by correlating some or all the antenna elements on theaerial array—finding the phase of the signal from each ground station bytrialing many different relative delays to the signals received at eachground station and finding the delays that maximize the signals receivedfrom each ground station. This tunes the range from each individualground station to the aerial antenna to give a much more precisedistance within the volume defined by the first (e.g. differential GPS)method. By having multiple ground stations and finding their moreaccurate ranges then the intersection of those ranges gives the platformand antenna position.

Because the modes of freedom for the array are three normal distanceaxes, at least three ground stations are needed to fully determine theaerial antenna position sufficiently accurately utilizing this aspect ofthe invention for the process of cooperative inter-antenna beamformingto be possible. If the orientation of the aerial antennas is also to bedetermined by this method then a further three ground stations areneeded to determine these. Alternatively, the antenna orientation can bedetermined by using on board orientation equipment—for example suitablegyroscopes.

Instead of using particular ground stations, dedicated beaconarrangements can provide the positioning signals.

By correlating the signals from the antenna elements at a sufficientfrequency and using short-term position prediction, knowing theapproximate platform (particularly if it is an aircraft) speed,direction, and roll, yaw and pitch rate, the position of the aerialantenna elements can be determined to the required accuracy forcooperative beamforming notwithstanding movement of the aerial antennas.

The same process can be used in reverse, transmitting signals from theaerial antennas or antenna elements to the multiple ground stations.

Once the aerial antenna elements are located in this way, all theirmovements can be tracked. However, in an additional aspect of theinvention an accurate local time measurement is needed to allow signalphases to be determined at the required frequency to ensure a reasonablecomputational load for the processing system with processing eitherlocally on the platform, or at one or more processing centres or somecombination of the two. If, for example, updates are necessary then thetime measurement is preferably accurate enough for the period betweenupdates to allow the position to be measured to less than 1/10^(th) of awavelength (at 2 GHz this would be to within 50 picoseconds).

In an alternative embodiment of the invention, cooperative aerialinter-antenna “beamforming” can be used in conjunction with manydifferent specific technologies for wireless communication to improveresistance to natural interference, jamming, or noise or to limit powerflux density. These technologies include amongst others, local wirelessarea technology (WiFi), as based for example on the Institute ofElectrical and Electronics Engineers (IEEE) 802.1 standards or “wirelesslocal area network” (WLAN). They also utilize various “spread spectrum”techniques in which the signal is transmitted on a spectrum larger thanthe frequency content of the original information, includingfrequency-hopping spread spectrum (FHSS), direct-sequence spreadspectrum (DSSS), time-hopping spread spectrum (THSS), chirp spreadspectrum (CSS), and combinations of these techniques.

In a preferred embodiment of the invention, cooperative aerialinter-antenna “beamforming” linked to appropriate backhaul facilities,can be utilized where high sustained or peak data rates are neededhitherto only associated with close or actual connection with fibreoptic cable. Such data rates of many tens of Mbps, more especiallyhundreds of Mbps or above are needed for outside broadcastingapplications, ultra high definition video and games applications andsimilar applications.

The position and orientation of the aerial antenna elements is sharedthrough the processing system for beamforming calculations.

The invention will now be illustrated by way of example particularlywith reference to an implementation referred to as “HAP-CELL”, whichutilises cooperative aerial antenna beamforming, and with reference tothe following figures in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a system according to theinvention.

FIG. 2 is an illustration of a phased array.

FIG. 3 illustrates beam forming on a single phased array.

FIG. 4 illustrates beam formation by a constellation of antennassupported by aircraft.

FIG. 5 is a schematic representation of the system arrangement andconnection with a mobile telecommunications network.

FIG. 6 is a schematic arrangement of an aircraft communication system.

FIG. 7 is a schematic arrangement of a backhaul ground based station (BGStation) system.

FIG. 8 illustrates multiple HAP-Cell systems.

FIG. 9 illustrates multiple platforms supported by tethered aerostats.

FIG. 10 illustrates the ability of this system to track UE within abuilding.

FIG. 11 illustrates an example of how beams from one or more aerialantenna(s) can be modified to give good coverage up to a nationalboundary but minimize energy spillover.

DESCRIPTION

A glossary of terms is described in Table 3.

The present invention can provide high data rate communications to andfrom UE that can interface with a conventional mobile telecommunicationsnetwork or Internet.

The invention allows for the support of standard interfacespecifications and protocols or proprietary interface protocols. In theillustrative example, there is support for communications with standard,unmodified mobile phones, smartphones, tablets or mobile computers asthe UEs. Other UE that could be supported would be transceivers onvehicles, vessels or aircraft, or fixed devices on or inside buildingsto enable the connection of electronic devices to the Internet.

The present invention is furthermore capable of connecting to thepre-existing mobile phone network and Internet through appropriateinterfaces. The communications topology can be arranged in the samefashion as a conventional mobile phone network, and in that case, thepresent invention can be used as part of a conventional mobile network.

FIG. 1 is a schematic representation of the present invention. FIG. 1illustrates just one potential configuration: utilizing multipleaircraft (8) as the platforms to create the constellation of antennasover e.g. approximately a 60 km diameter “Service area” (13).

The system uses a “constellation” of antennas mounted on multipleplatforms (9) operating at approximately 20 km altitude. These platformscan be, for example, aerostats, tethered or free flying; or manned orunmanned aircraft. In the case of aircraft, they can, for example, besolar powered for long endurance at suitable latitudes and seasons, oruse hydrogen as a high energy density fuel for applications that requirehigher-powered equipment or in areas that have limited solar irradiationat particular seasons. Other fuels such as hydrocarbons can be utilized.

In FIG. 1, each aircraft platform (9) supports two antennas (15,16), oneused for transmission and one for reception. In one embodiment, theplatforms carry phased array systems, or horn antenna systems. Thesesystems, when using beamforming technology, can provide many separatebeams (6,7) in different directions to communicate with UEs (11)situated on different “patches” (10), areas illuminated by an antennabeam, and can also provide the “backhaul” links (5) to the “backhaulground”, BG stations (4).

The invention can provide communication links with BG stations (4) toprovide the backhaul data communication systems that support the UEactivities with the rest of the cellular network. The BG stations canalso use phased array systems with beamforming technology to communicatedirectly with the platforms under the control of a computer processingsystem, e.g. a ground-based computer processing centre, or simpler dishor horn-based systems. The BG stations can be connected to theground-based computer processing centres (1) via standard protocols; byfibre optic, or microwave connections or any other physical connectiontechnology (3). For simplicity not all the links to the backhaulstations are shown in FIG. 1.

An illustrative embodiment of the present invention, as shown in FIG. 5includes:

-   -   1. The platform based phased array antennas, which communicate        with the many UEs (UE₁, UE₂ to UE_(m)) and BG stations (51,52)        supported by aerial platforms (not shown).    -   2. Optional additional platform based receivers and transmitters        that carry the backhaul data links (not shown).    -   3. The BG stations or other antennas which communicate with the        platforms and link to the processing centre.    -   4. A processing centre (53), which calculates all the parameters        for the communication links and provides the interface to the        wider cellular network. (54).

Thus, the present invention provides that a constellation of antennas(normally at least three, but typically fifteen or even many hundred inline of sight within the area in which the ground based UE resides)provide co-operative or inter-platform beamforming for very targetedcommunications with individual users, see FIG. 1: the beam (12) used fora single user within a particular patch is very small.

Utilizing the invention a targeted beam may be formed on a single UE:the intersection of this with the ground can be presented to the mobilenetwork as an individual cell which has the ability to use the fullavailable resources (signal bandwidth and communication power) forcommunication to a single piece of UE. These cells are termed herein as“dynamic femtocells” or DF-Cells.

FIG. 10 illustrates the ability of this system to track UE within abuilding. A constellation of aerial antennas supported by aircraft(111), are situated above a building (112) in which there are two UEs (1and 2) (110). In this illustration each aircraft shown represents anumber of aircraft. If the building walls and roof are relativelyimpervious to the radio wavelength being used for communication,communication will depend on radio signals being transmitted andreceived through windows and other apertures. In this case only antennasin line of sight of UE 1—within the cone defined by 1 i or thereflection from the floor from UE 2 within cone defined by φ₂ willcontribute significantly to communication. It is therefore importantthat the choice of antennas used and the weights and phases allocated tothe antennas generate beams from the antenna constellation that canreflect the local conditions to the UE to allow beams of an appropriatedirection and position.

Such choices can improve the signal strength at the UE and reduce theexpenditure of otherwise wasted energy on the aerial platforms, therebyincreasing endurance or power available for other communication needs.By using the process or network according to the invention, high datarates in excess of 100 Mbps to or from individual UEs are possible.

The communication of particular data, applications and content may havedeleterious effects on user equipment or particular users, for example,children. The present system allows a system operator to introducechecks in the processing centre or elsewhere on data, applications andcontent to protect user equipment or particular users.

Thus, in a further aspect the invention relates to a method of receivingand/or transmitting data, applications and/or content to an antenna onuser equipment, the method utilising the network or process as describedherein.

The present system allows for much more precise identification ofgeographic location within a wide area of coverage, along with higherdata rates, than current systems.

Currently in macrocells outside urban areas other than by using anadditional system such as differential GPS, locations are difficult toestablish to less than tens if not hundreds of metres. Even within urbanareas with microcells locations of 10 m or less are difficult to obtain.

Within a large area accessible by a constellation of antennas, locationcan often be identified within metres and even to sub-metre resolution,dependent on propagation conditions. This allows the system at theresolution of rooms or buildings the capability to restrict access tospecific or general user equipment on a continuous or intermittentbasis.

Such an access capability has the potential to allow appropriateauthorities within properties over which they have suitable rights torestrict or modify access, for example to control under age or visitoraccess in specific rooms, at specific times or continuously. Thiscapability also has the ability to readily provide information on thelocation of the user equipment to another party contacting another pieceof user equipment.

In a preferred embodiment, the invention relates to a process for themanagement of access to the apparatus or process described herein, byspecifying the location and/or time that will permit or reject thetransmission or reception of information to that location.

Phased Array Antennas and Inter-Antenna Beamforming Technology

The UE may include transmitters or receivers or both. The aerialantennas can be phased arrays or conventional antennas or both.

As discussed above, in a preferred embodiment, the present inventioninvolves the use of advanced phased arrays, which enable “intra-arraybeamforming” or beamforming within a single antenna. There follows abrief description of these technologies.

Phased arrays consist of a large number of individual antenna elements,but in the rest of this document “antenna(s)” will refer to one or morephased arrays or one or more conventional individual antenna(s) such asa horn antenna(s).

Phased arrays have a particular advantage for high altitude aircraft andother platforms in that their aspect ratio, the ratio of their width todepth is generally low, and thereby often easier to mount in a structurewhere low aerodynamic drag is required.

Antenna(s) mounted on high altitude platforms can communicate both toand from UE, not primarily connected other than via the high altitudeplatform antenna(s) with a large ground based communication network suchas the internet or a cellular network. Such antenna(s) can alsocommunicate with backhaul ground based stations (“BG stations”) whichare directly connected to a large ground based communication network andprovide “backhaul” known to those skilled in the art.

The UE may include transmitters or receivers or both. The aerialantennas can be phased arrays or conventional antennas or both.

FIG. 2 is an illustration of a small phased array (21). It has an arrayof small antenna elements (22), which are connected to either the inputof low noise amplifiers prior to digitization as a receiving system orto output amplifiers for transmission. Each antenna element is usedindependently and by controlling the precise time, or phase, of a signalbetween elements then a beam can be formed in a similar fashion as witha parabolic dish. The phased array may be designed so the antennaelements are all planar as shown in FIG. 2 where two or more layers (23)define the electromagnetic performance. The phased array can also be amore complex shape for example, “bowed” so that the outermost elementsare pointing at an angle to the axis of the array.

The mechanism to form beams from a single receiving phased array isshown in one-dimension in FIG. 3, which shows beamforming on a singlearray. Phased-array beamforming is a well-established and understoodtechnology and this invention supports phased array antenna concepts. Byway of illustration a specific realisation is considered in which eachantenna element (36) is at a distance (37) from its neighbour of lessthan or equal to half the wavelength of the highest operating frequency;in the example shown in FIG. 3, which is designed to operate in the 2GHz bands (λ=15 cm), the spacing (37) is ˜7.5 cm. This enables the arrayto detect the amplitude and phase of the received electromagneticsignal. Each antenna element is connected to a low noise amplifier. Inorder to form a beam for a flat array, the requirement is to have alinearly increasing signal delay across the width of the array; this canbe done in either the analogue or digital domain. The diagram at the topof FIG. 3 shows the relative delays (32) on the y-axis (30) used inproducing the beam (35) where the distance across the antenna is plottedon the x-axis (31). The signals from all the antenna elements suitablyrelatively delayed are then summed to form a composite signal, which isa “beam.” The beam size is given approximately by λ/d where λ is thewavelength and d the diameter of the array. In the case of a 2 GHzsignal and a 1.5-metre diameter array, the beam would normally be ˜5.7°wide. However, by appropriate antenna element “weighting” this can betailored to widen the beam. If required this enables the beams to bevaried to give approximately uniform coverage on the ground as changesin the elevation of the array from points on the ground result in thebeam being spread to a greater or lesser extent over the surface.

Phased arrays also have the benefit that, by using recent developmentsin digital technology, very wide bandwidths can be implemented. Thefrequency range of recent, planar antenna elements can be as high as 3:1from the lowest to the highest frequency supported. In such planarsystems multiple conducting or partially conducting layers are eachsituated in planes parallel to each other and at 90 degrees to the axisof the antenna.

Because all the signals from each antenna element are available for anyusage, it is practical to apply a different set of delays across thearray and sum the second set of signals and form a second beam. As alsoillustrated in FIG. 3: another beam (34) can be produced by a differentset of delays (33). This process can be repeated many times to form manydifferent beams concurrently using the array.

Forming many beams in the digital domain can be readily achieved, theonly requirement after digitization is additional processing resourcesand data bandwidth to communicate or further process all the beaminformation.

While it is possible to form a large number of beams with an individualphased array, the maximum number of “independent” beams that can carrydata unique from all other beams cannot exceed the total number ofantenna elements in the array. For example, if an array has 300independent antenna elements (separated by ˜λ/2 or greater) there can bea maximum of 300 independent beams; more beams than this can be formedbut these beams will not all be independent. In this instance thenon-independent beams will each transmit and receive the same (orsimilar) encoded information—these beams may still be utilised byappropriate resource sharing schemes or in other ways relevant to theinvention.

Phased arrays can form beams over a scan angle range up to approximately±60° from the axis normal to the plane of the array. This is due to thegeometrical limitation of the array where the illumination area of theelements is reduced as a cosine of the scan angle; also the sensitivityof the beam of the individual antenna elements is reduced due to theirbeing off the centre of the beam. The result is that the illuminationarea of a horizontal array is limited by the maximum scan angle toapproximately 60 km diameter with large single arrays for transmit andreceive, and this limit may be extended with more complex shaping of thearrays.

Referring to FIG. 6, the receiving array may consist of many planar dualpolarized receive elements (68) in a regular array (64). Twopolarisations are preferred for the inter-antenna beamforming techniquesdue to the need for precise amplitude and phase information; also toensure the best signal reception at the arbitrarily positioned UE. Eachpolarization is amplified, filtered and digitized over the receivebandwidth required. The antenna element electronics are convenientlymounted immediately behind the receive antenna element for low noisepickup, simpler assembly and to distribute the heat load over a largearea. The digitized signal for each polarization is transmitted to thesignal processing system for beamforming.

In one example, the array is 1.5-metres in diameter with antennaelements spaced at 7.5 cm. This results in approximately 315 antennaelements or 630 signal paths. This gives a service area of 60 kmdiameter broken into ˜160 patches (concepts for a modified array thatcan cover a wider area are discussed later in this document).

A position detection system (60), an orientation detection system (62)and a control and coefficient processor (61) interface with a signalprocessing system (63) which, in this preferred implementation, needs ahighly accurate clock system (66) which can be interfaced in turn to aPositioning System (67).

The transmit array (65) is of a very similar design and size as thereceive array. It has many dual polarized transmit elements (69).Digitised signals are computed by the signal processing system for eachpolarization, transmitted to a digital-to-analogue converter, filtered,amplified, and passed to the output power amplifier for transmission. Aswith the receive array, the element electronics can be mounted behindthe transmit elements to distribute the heat load and minimize strayradiation.

Beamforming

The present invention utilises beamforming across the multiple aerialantennas to generate narrow cooperative beams to the UE.

The system operates by the antennas, e.g. phased arrays on everyplatform in a “constellation” of multiple arrays each forming one oftheir component signals onto a specific “patch”. The signal that is sentfrom all the arrays to a specific patch carries essentially the sameinformation content (differences could include e.g. noise fromquantisation and analogue effects), but has a phase delay across theconstellation of antennas, thereby forming a very narrow “synthesizedbeam” from the individual array beams.

The phase delay, or time delay for wide band signals, for the datasignal from each antenna to a UE is compensated accurately for thedifferent distances in phase space from individual antennas to the UE.The delay is calculated such that the signal to the UE from everyantenna arrives at the same time and is phase coherent at the UE. Signalamplitude from each of the aerial platforms is adjusted such thattypically all signals are normalised at the UE, but can be adjusted, forinstance to reduce side lobes. These adjustments are known as the“beamforming coefficients” for each signal. A similar process is appliedto the signal to each UE within a patch and combined to form the overallpatch beam for every aerial antenna. These beam forming instructions caneither be calculated on the ground in a processing centre andtransmitted as an encoded representation of the patch beam to eachaerial antenna or used at the platform to form the patch beams.

For signals transmitted from the UE to the constellation of aerialantennas the processing system similarly applies phase or time delays tothe patch beam from every aerial antenna in the constellation and thensums them to form a coherent receive beam on a UE. This combined signalis used to communicate with the wider cellular network. Typically thisprocessing will be carried out at the ground processing centre whichreceives an encoded representation of the patch beams received at theaerial antenna.

The synthesized beams are computed to become “user beams” which trackspecific UEs. This is illustrated in FIG. 4, which shows beam formationin the service area, by a constellation of antennas labelled HAP₁, HAP₂to HAP_(m). The antenna on HAP₁ is shown producing three beams (40,42,and 44), which are directed at three patches (41, 43, and 45). HAP₂ andHAP_(m) are shown producing similar beams.

The size of the synthesized beam is much smaller: ˜λ/D where D is themaximum diameter of the constellation of antennas. If, for example, theantennas are situated within a circle of diameter, D=10 km, at thecentre of a service area of 60 km diameter, then for a 2 GHz signal thebeam is only 0.1 arc minutes wide; which results in a beam diameter ofonly 60 cm diameter at ground level directly underneath the antennaconstellation or less than 3 metres diameter at the edge of the servicearea. The small size of the area these user beams interact with is shownby the areas (46).

The minimum size of the area on the ground, the “resolution area,” whichan independent beam from a single aerial antenna could interact with,varies with its position relative to the aerial antenna. The “maximumbeam data rate” (MBDR) that can be transferred to or from a singleantenna within a beam is given by the number of bits per second perHertz bandwidth, multiplied by the bandwidth available. The maximumnumber of bits per second per Hertz is limited by the signal to noiseratio of the signal, as is well known to those skilled in the art.

The beam sizes can be adjusted to be larger than the minimum beam sizefor a single antenna, so that area illuminated by each beam may betailored to the requirements of the operational environment of thesystem.

If all the aerial antennas are relatively close together compared to thediameter of the service area, the “resolution areas” will be comparablein size from one antenna to another. If the aerial antennas are farapart, the “resolution areas” from different antennas will be verydifferent in size. The limit to the amount of data that can betransferred within one resolution area is given by the number ofantennas in the constellation multiplied by the MBDR if the resolutionarea sizes from each of the antennas are similar. The availablebandwidth can be split into multiple blocks of resources, e.g. frequencybands, time slots and codes, thereby increasing the number of UEs thatcan be supported although with a lower data rate available to each UE.Other radio resource sharing techniques can be used. There cannot bemore data present in the user beams than is available in the antennabeams.

By use of the present invention the constellation of aerial antennaseffectively operates just as would a single antenna having a dimensionthat is from 1 to 30 kilometres, preferably from 5 to 20 kilometres.Thus, very narrow beams can be generated.

Weightings on the antenna elements can be varied to control ground basedpatch sizes based on an optimization function reflecting populationdensity or data rate density, taking into account the orientation andattitude of the antenna platform(s). In this manner if the centre of theconstellation is over a large city but at the edge of the service areathere is a low population density, beams to and from the constellationmay involve only a small fraction of the antenna elements of each arraythereby saving power.

Platforms Supporting Antennas

Platforms can be implemented as:

(i) Aircraft that are powered using either solar energy or hydrogen orhydrocarbon fuel to carry the communications equipment at approximately20 km. The aircraft carry the equipment for communicating with UEs andwith the BG stations. Also, they carry the signal processing systems,precise clock and timing units and control computers.

(ii) Free flying aerostats powered by solar cells or other technologies.The aerostats carry the equipment for communicating with UEs and withthe BG stations. Also, they carry the signal processing systems, preciseclock and timing units and control computers.

(iii) Tethered aerostats powered by hydrogen conveyed along the tether,or supplied with electrical power via the tether or supplied by solarcells situated on or connected to the aerostat platforms. A tetheredaerostat supporting one or more tethers can carry a number of platformsat a number of different altitudes with each platform in turn supportedby the tether(s). Each platform may also receive additional support fromits own aerostat. The tethered platform system carries the equipment forcommunicating with UEs and with the BG stations, and they may carry thesignal processing systems, precise clock and timing units and controlcomputers or this may be ground based. FIG. 9 shows the layout of such asystem.

In the case shown there are tethered aerostats (90, 91) connected bytethers either directly to the ground (93) or indirectly (92). Someaerostats (91) are connected indirectly, and some directly (90) to theground. In the case shown the antennas (94) are wholly contained insidethe envelope of the aerostats. They may be partially contained or notcontained at all. UE (96) is communicated to by beams (95) from theaerial antennas (94) in a co-operative manner. At least two antennascommunicate with each UE.

(iv) Ground-based antennas based on very high towers or buildings wherethere is significant movement of the antenna of at least 1/10 of thewavelength of the carrier signal.

(v) Conventional commercial aircraft used for passenger transportsupporting additional intermittent aerial antenna capability.

(vi) Space-based satellites.

(vii) Hybrid air vehicles.

The system may consist of one or several types of platform describedabove.

Platform Communications with UE

The platforms are normally all equipped with at least two phased arraysof equivalent size and number of elements, a transmit array and areceive array, to enable the system to have concurrent transmission andreception for any waveform and multiplexing technique that operates atthe selected frequency allocation and bandwidth. It is possible to use asingle array, but the electronics required is of greater complexity andweight, and may only support time division multiplexing and not the moreusual frequency division multiplexing. The arrays form beams that dividethe service area into a number of patches. The patches are treated as“cells” by the cellular telephone network.

The UE may be ground based or could be on a manned or unmanned aircraftat lower altitude than the aerial antennas. The UE could also be carriedon some form of transportation technology including but not limited totrains, motor vehicles and shipping.

Backhaul Communications

The system of the present invention can provide a “transparent” linkbetween the cellular network and the individual users' devices in asimilar fashion as conventional ground based mast based systems. Thisprovides compatibility with the existing cellular network.

The present invention allows for the possibility of a substantial amountof data communicated between the platforms and the UEs. Thus there hasto be at least the same amount of user data communicated through thebackhaul system to and from the platform and processing system. Thefollowing are some options for transmitting the data from and receivingit to the platforms via the following communication links:

-   -   1. Use capacity on the phased arrays used for communication to        UE on each platform    -   2. Use alternative, high capacity links on alternative phased        arrays    -   3. Use single beam point-to-point high capacity links    -   4. Use free-space optical links to BG stations.    -   5. Use free-space optical links between platforms, so that a        platform in a less well-developed area can communicate by laser        to a satellite or aircraft that has a microwave downlink to BG        stations. This can be via a series of repeater platforms with        redundancy.

Both polarisations could be used independently on the backhaul link,potentially halving the number of BG stations required.

The embodiment described below will use implementation 1 above and shareresources on the large arrays to provide both the backhaulcommunications and the user links.

Much of the technology used in the present invention is used in thetelecommunications industry and develops techniques used in radioastronomy for beamforming and beam shaping. The use of one-dimensionalphased arrays, the interface specifications, the data encodingtechniques, the use of signal processing etc. are all widely used by theexisting cellular telecommunication systems. The present inventionintegration results in a very high performance system that interfacescompatibly into most existing cellular telephone network technology.

Processing System

The present invention is managed by a processing system, which may be adistributed system or, as shown in the figures, FIG. 1 shows aprocessing centre (1), which is normally ground based, saving weight andpower on the aerial platforms. The processing system interfaces to thecellular telephone network (2), and it provides direct control of thesignals being used by the platforms to communicate with the UEs.

The processing system may be physically distributed between a processingcentre, processing co-located with the aerial antennas and/or backhaulground stations, and processing services provided by third-party (knownas “cloud”) providers.

The processing system provides the interface to the cellular networkthrough a defined interface to the cellular network.

The processing system computes for the aerial antennas:

(i) The beamforming coefficients required for the signals received fromthe UE and BG stations both for antennas and if these are phased arrays,normally but not exclusively the coefficients for the antenna elements.

(ii) The phases and amplitudes for the signals to be transmitted to UEand BG stations.

(iii) All algorithms to implement operational aspects such as positionaldetermination of platforms and user equipment.

For BG stations the processing system can compute and provide

(i) The coefficients for the signals to be transmitted by the BGstations to the aerial antennas.

(ii) The coefficients for the signals received from the BG stationantennas and if need be the antenna elements if the BG stations areusing phased array antennas.

The BG stations can be linked directly to a processing centre viahigh-speed connections such as fibre optic data links or directmicrowave links.

The signals at the platform are complex in that they define all thecharacteristics to enable the constellation of platform phased arrays tobeamform precisely onto individual users.

All these signal processing and beamforming calculations are performedin the processing system. The processing system may comprise at leastone processing centre with some processing required on each platform.Such processing centres are ideally located at ground-level, forsimplicity. Preferably however, ground level processing dominates theoverall signal processing capability, consuming over 70 percent,preferably over 90 percent of the signal processing electronicselectrical power requirements.

The processing system also determines how the system presents itself tothe cellular network, including providing the required interface toenable efficient resource allocation.

The processing system may be capable of a further range of enablingfunctions, as will now be illustrated. The processing system may becapable of determining when the formation of a DF-Cell is required topermit up to the maximum resource allocation to a given piece of userequipment. The processing system will support all resource allocationmethods required by the cellular network including, but not limited to,frequency and time multiplexing. The processing system will alsodetermine the frequencies that will be used by each platform. This canbe up to the full bandwidth of the frequency allocations or restrictingthe bands for specific network or mobile phone operators using eitheroverlaid systems according to the present invention or a mixture ofground based antennas and the present system. It would also supportco-operative use of multiple operators, assuming suitable agreements canbe reached.

The system can also use time division multiplexing or other radioresource sharing techniques.

Programmable signal processing components, Field Programmable GateArrays, FPGAs, are now of a power and capability suitable for thissystem. Such devices are now available that can perform this task, e.g.the Kintex(http://www.xilinx.com/products/silicon-devices/fpga/kintex-ultrascale.html)family of devices from Xilinx, which feature up to 8 Tera MACs(Tera=10¹²; MAC=Multiply Accumulate, the basic processing operation indigital signal processing) processing capability and 64×16 Gb/scommunication channels using modest power, typically under forty watts.

The signal processing system uses information transmitted from theprocessing centre to form required beams on the UEs and (if required) onthe BG stations. The data in the beams that are formed is retransmittedto users, BG stations or used by the control processors on the aircraft.

As discussed, processing on the platforms is preferably minimised,however there may be at least some processing carried out there whichcan include:

-   -   Reconstruct the coefficients used by the signal processors to        form the required beams;    -   Use information from the position and orientation systems as        part of the beamforming process;    -   Monitor, control and report the status of the aircraft payload        systems.

The processing capabilities required are of the order of a conventionalPC server, but as a specialist implementation requires less power.

Accurate time determination at the moving aerial antennas is essentialto the precise reception and transmission using beamforming of thesignals.

It has been found that a suitable clock generation uses a GPS system forlong-term (greater than ten's of seconds) accuracy and an oventemperature stabilized crystal oscillator for short-term accuracy. Thiscombination will give the phase precision required for both localaircraft beamforming and beamforming between aircraft. The requirementis to have phase stability for the analogue to digital converters, ADCs,and digital to analogue converters, DACs, to have precise sampling atall times.

Backhaul Ground Stations (BG Stations)

As discussed, the present invention may benefit from the provision ofone or more BG stations. The BG stations can provide the communicationlinks to and from the platforms and the processing centre. Each BGstation should be able to communicate independently with as manyplatforms in line of sight as possible, to maximize the data ratecapabilities of the platforms.

Typically, there are therefore at least as many beams formed at each BGstation as platforms visible from the individual BG stations. Usingphased arrays as the communication system at the BG stations willprovide this facility. The design of these phased arrays can be similarto those on the platforms.

BG stations can provide the high-speed data links between the aircraftand the processing centre. To reduce the number of BG stations and theirassociated costs, it is useful for the BG stations to have multi-beamingcapability so that they can each communicate with each aerial antennaindependently when there is a constellation of multiple antennas, toprovide the high data rates required for the network. By this means thedata rate to or from each BG station can be increased by a factor equalto the number of aircraft being communicated with over that which wouldbe possible with a single aircraft.

An implementation using phased arrays similar to the systems used on theaircraft is illustrated in FIG. 7. As with the aircraft phased arraysthere are separate transmit (75) and receive (74) arrays.

The receive array (74) has a large number of elements (78) which providesignals to the receiver processing system (72). The transmit array (75)has a large number of elements (79) which receive signals from thetransmitter processing system (73). Both receiver and transmitterprocessing systems interface (71) with the processing system (70). Theyalso can require input from a clock system (76), which in turn receivesinput from a positioning system (77). BG stations are separated farenough apart for beams from the individual aircraft arrays to resolvethem independently with different array beams. This is to provide asufficient aggregate data rate to every aircraft.

In the example shown, BG stations are under the direct control of theprocessing system; the processing system determines the amplitude andphase for every array element.

In certain locations where the availability of BG stations is low, itmay be advantageous to link one aircraft with another more suitablylocated over BG stations by laser or free space optical devices. Thesehave been developed in recent years and allow high data ratecommunication (greater than 1 Giga bit per second) with modest (under100 W) power consumption and can be of modest weight of less than 25 kgbut able to communicate in the stratosphere at distances of at least 60km, and more preferably of 250 km and on occasion of 500 km or more.With such an arrangement it is possible for one or more aerial antennasto be linked to BG stations many hundreds if not thousands of kilometresdistant by utilizing laser links between additional aircraft.

Aircraft Based Communication System

For communicating with the UEs the aircraft are fitted with large phasedarrays and associated signal processing and control systems, asillustrated in FIG. 6.

There are two phased arrays: one for receive (64) and the other fortransmit (65). This is to ensure that there is full separation betweenthe two paths such that both systems can operate using frequencydivision duplex, FDD, systems; these are the most popular cellular phonecommunication links. Two arrays can also support the alternative timedivision duplex, TDD, systems without the complexity of sharing an arrayfor both transmit and receive.

As discussed above, these arrays both have many individual receive ortransmit elements (68, 69); the array signals are combined in the signalprocessing system (63) to produce the required beams.

Finding the Position and Tracking Users During a Connection

The system can keep track of UEs in a similar fashion to a conventionalground based network. The UE needs to be kept within the cooperativebeam when a call or data transfer is in progress.

When using Inter-Aerial Antenna beamforming the beam on the UE could bevery focused, e.g. of approximately 1 metre diameter. There are then twofurther functions required:

-   -   To sufficiently identify the required antenna weightings to        allow such a focused beam to establish a connection;    -   To adjust these weightings appropriately during the connection        to allow for the movement of the aerial antennas and the UE.

It has been discovered that by using the arrays within the constellationto “focus” on the UE by using progressively more and sometimes differentantennas as part of the beamforming process such a process can beachieved. By optimizing the beamformed location for signal strengthprior to including more aircraft, then the relevant antenna weightingscan be optimized. The focusing process can be speeded up substantiallyby the UE reporting its GPS position, if that function is available.

During a connection the UE can move out of the beam. Narrow bandwidthsecondary beam(s) can be used to rapidly sample in a pattern around theuser's position. Increased signal strength in a particular direction orarea can then be used to modify antenna weightings and beam position anddirection.

Thus, in a preferred embodiment, the first cooperative beam is generatedat a first point in time, and at a second point in time, carrying out asecond beamforming operation to ensure that the cooperative beam isdirected to the position of the moving user antenna.

Beam Shaping and Sidelobe Minimization

The requirements of beam precision for cellular networks are quitestringent, particularly for energy spillover at national boundaries. Agreat benefit of using phased array techniques rather than fixed dishesis the ability to modify the beams electronically.

Setting the appropriate amplitude and phase delay on the antennaelements forms and steers beams. When there are many antenna elements,this gives flexibility in shaping the beam to the specific requirementsby trading off sensitivity and beam control. The result is that thepatches can be well defined and the edges of the service area can becontrolled closely to minimize sidelobes or other artefacts to affectneighbouring areas.

FIG. 11 illustrates an example of how beams from one or more aerialantenna(s) can be modified to give good coverage up to a nationalboundary but minimize energy spillover into an adjacent country.

In diagram 130 in FIG. 11, patches of coverage beams from individualantennas or multiple antennas follow a regular grid arrangement wherethe position of the grid elements is given on the x-axis (133), in thiscase East-West, by numerals and on the y-axis (132), in this caseNorth-South, by letters. For example the element 136 can be referred toas having location G7. An irregular national border is shown (135).

Shaded squares illustrate to where energy is being transmitted by theaerial antenna system. It can be seen that to ensure low spillover ofenergy there is an area next to the border where little energy istransmitted, for example in patches A6, B7, C7, D5, E5, F8 and so forth.

In diagram 131 in FIG. 11 shows the same area, with the same y-axis(132) and a comparable x-axis (134) but with modification of the antennaelement and antenna phasing—and if need be amplitude, to move thepatches to the left or right to more closely follow the national border.For example cell G7 (136) has moved, along with its row (G1 to G5) in aneasterly direction so it has become located at a new position (137). Theuncovered area closer to the national border has been significantlyreduced.

The synthesized beams formed using Inter-Antenna beamforming can besimilarly controlled, trading sensitivity for beam-shape to minimizeartefacts and actively control beamsize.

Data Rates

The data rate available depends upon the bandwidth available from theband that is in use. For this embodiment, it is assumed that the band isLTE Band 1 (other frequencies are also available):

Uplink: 1920 MHz to 1980 MHz 60 MHz bandwidth Downlink: 2110 MHz to 2170MHz 60 MHz bandwidth

In certain embodiments the links to individual UEs will only use thebandwidth required for the function being used, hence the bandwidth canbe sub-divided to service as many users as possible.

The data rates through an example HAP-CELL system are shown in Table 1.As can be seen, this is using Band 1 frequencies and 50 aircraft in afleet. The data rates per link are dependent upon the signal to noiseratio of the link; hence there is an expectation of higher data rates inthe same bandwidths for the backhaul links than to the UEs. This isbecause the connection to the backhaul can be much better managed due tothe fixed, outdoor nature of the equipment and the potential for usinghigher transmission power and larger antennas than for mobile UE.

As can be seen, the maximum data rate to the UE is very high, assumingthe use of clear, high SNR connections. As with all cellular networks,the data rate will be adjusted for the actual link performance.

There is a very strong trade-off of the number of BG stations and thepower that can be used for each link. It is worth noting that thedominant data communications will be between the network and the user,with typically a lower data rate on average on the return path. Thismeans that a higher power can be used from the ground stations to theaircraft for a higher number of bits per Hertz for a better spectralefficiency; also, a higher power for transmission from the aircraft thanis used by the user for enhanced data rate on that link.

Use of 28/31 GHz Bands

There are frequency bands at 28 GHz and 31 GHz allocated by theInternational Telecommunications Union to HAP downlink and uplinkcommunications as follows:

Downlink: 27.5 GHz to 28.35 GHz 850 MHz bandwidth Uplink: 31.0 GHz to31.3 GHz 300 MHz bandwidth

These provide considerably more bandwidth than the 2 GHz frequenciescommonly used for mobile networks, but are harder to implement withconventional electronics—particularly as a phased array.

TABLE 1 Example HAP-CELL system, 50 aircraft, 1.5 m 2 GHz single arrays(values used for indicative sizing of the system) System Value CommentsNo. of Aircraft 10 to 50 Aircraft in a single fleet No. of BG stations157-416 This depends upon encoding and number of polarisations onbackhaul links. Bandwidth 60 MHz LTE Band 1: Chosen band forillustration purposes Wavelength, λ 15 cm ~2 GHz Aircraft height 20 kmLower stratosphere and well above commercial airspace Service areadiameter 60 km Within max. scan angle of aircraft phased arrays allowingfor pitch and yaw of aircraft Platform mounted phased array: Diameter1.5 m Selected to fit on the aircraft with good performance Number ofantenna elements 315 ~1.5²*π/(4*(0.075)²). (Area of array)/(area ofantenna element) Polarisations 2 Dual polarization for beamforming andhigh reliability for user links Max. antenna scan angle 60° Physicallimitation, 20tan(60°) = 34.6 km, defines Service area No. of arraybeams formed ~160 50% × number of antenna elements: The number ofpatches is restricted for good definition of the edges. Patch size 4.7km × Defined by the size of the arrays 4.7 km Backhaul data links:Implementation Phased Uses additional virtual patches on the aircraftphased array arrays beams Polarisations 2 Dual polarization, forbeamforming performance. In principle could use separate polarisationsfor data-but not considered here. Modulation 256-QAM 8-bit/symbol. Datarate per link (max) 480 Mb/s 8-bit/s/Hz * 1 polarisations Data rate perlink (min) 360 Mb/s 6-bit/s/Hz (64-QAM) * 1-pol Data rate per BG station  18 Gb/s Direct communication with 50 aircraft (in this example)- 1Polarisation User data links: Patches 160 For a 60 km dia. service areawith 1.5 km patches Polarisations Identical Identical information toavoid phone orientation issues Modulation, max Up to 64- 6-bits/symbol.This is the fastest modulation on very good QAM links Modulation,average 2- The average data capacity per link. bit/symbol Data rate maxfor 1 user 360 Mb/s The absolute max data rate with full BW and 64-QAMData rate per aircraft (typ.) 19.2 Gb/s 120 Mb/s per patch * 160 patchesSystem Data rates: Data rate per patch, max   6 Gb/s 120 Mb/s per plane,50 planes Data rate over Service area, max  960 Gb/s Assuming 50 planesin fleet in line of sight

Power Requirements for Aircraft Payload

The payload power usage on the aircraft considered is for thecommunications arrays, the digital processing systems on board and thecontrol and positioning systems. Keeping the aircraft payload powerrequirements low is important for the limited power availability ineither the solar powered aircraft or hydrogen-powered aircraft operatingat high altitude.

For the phased array receivers and transmitters the power will scale asthe number of antenna elements. Performing as much processing as ispractical in the ground based processing facility minimizes theprocessing requirements at the aircraft. The power for the large numberof digital interfaces will dominate the processing power.

Estimates for power consumption are shown in Table 2. This is an examplecalculated for an aircraft incorporating two 1.5 m diameter phasedarrays for transmit and receive. Each array has 315 dual polarizationantenna elements; each array therefore has 630 signal channels. Thepower requirements are for ˜1.6 kW with these arrays.

The elements of the processing system located on the platform areimplemented using standard components and as such will benefit over timefrom the improvements in processing available per unit of powerconsumed.

This would scale almost linearly with the number of elements or with thediameter of the arrays squared. Hence 3-m diameter arrays would beapproximately four times this power requirement.

TABLE 2 Estimated power requirements for airplane with 2 × 1.5 m 2 GHzarrays Power Power each total Subsystem (W) Number (W) Comments Receivearray: LNA & gain chain 0.5 630 315 Digitisation & 0.2 630 130communications Power losses 45 10% power distribution losses Transmitarray: DAC & 0.2 630 130 communication Power amplifier 0.5 630 315Assuming 250 mW RF power per polarization Tx, 50% efficiency Powerlosses 45 10% power distribution Signal processing: Processing 200 10FPGA's at 20 watts (processing) each Signal transport 0.1 630 65Inter-FPGA links Control, clocks, orientation: Estimate 400 Substantialprocessing resources Total 1635

Effect of Aircraft Based Communications on Mobile Users

Communication links between aerial antennas and BG stations willnormally be at above 30 degrees elevation resulting in a consistentsignal for a given location. For UE the signals to and from the aerialantenna will often be passing through roofs of buildings, which willresult in significant losses. However, in large systems, with manyaircraft over adjacent, or overlapping service areas, then there is ahigh likelihood of signals coming in obliquely through windows andwalls, which are typically more transparent to the signals.

The aircraft are up to 35 km away and have a round trip link of morethan 70 km; the processing will have some buffering delays. The delayswill not add up to more than a few milliseconds which is well withincurrent mobile network specifications of <30 ms or proposed 5 Gspecifications of <5 ms.

Multiple Service Areas

The HAP-CELL system is intended for use over large areas. For denselypopulated areas, e.g. major cities, there may need to be multiple fleetsof aircraft serving multiple service areas. The system readily scales inthis fashion and economies of infrastructure and additionalcommunication capabilities become available. A multiple system isillustrated in FIG. 8.

There are three fleets of aircraft (85, 86, 87) identified. These formbeams on patches either in their unique illuminated area, e.g. (88) oroverlapping areas, e.g. (89). The cellular network and Internet (81)interfaces with one or more processing centres (82), which are linked byfibre optic cables or by microwave (83) to BG stations (84 or 841). Eachservice area (810, 811, 812) is approximately 60 km in diameter. As canbe seen, the service areas can overlap which provides higher total datarate for users. There is also the benefit of improved coverage, forexample, if a user is shielded from a fleet of aircraft by being on the“other side” of a building, then there is likely to be coverage from anadjacent fleet.

Due to the user beam from a fleet of aircraft being “private” to anindividual user there is no significant interference from adjacentfleets, or beams from adjacent fleets that are spatially separated.

There will be a significant saving in infrastructure. BG stations (841)can service more than one fleet of aircraft if they are suitablypositioned. The BG stations form beams to each aircraft within a fleet,consequently, provided the fleets are within range then a BG station canservice all the fleets within 30 km to 35 km.

The design of an area's coverage should consider how a number ofaircraft, e.g. 50-100, should be deployed in fleets to have maximumbenefit. There may be more, smaller fleets or fewer large ones withappropriate degrees of service area overlap. The details will dependupon the population density and other factors, but the HAP-CELL systemcan allow these trade-offs to be made.

Summary of Benefits of the Aerial Inter-Antenna Beamforming System

By using high altitude platforms and inter-antenna beamformingtechnology the present invention confers the following benefits overexisting mobile phone and communication systems:

Wide coverage area: The horizon for an antenna on a platform at 20 kmaltitude is at approximately 500 km radius. The elevation of such aninstrument from any particular location on the ground is defined as theangle the instrument is above the horizontal at that point. For theplatform to be above 5 degrees elevation, any location on the groundwill be within a circle of radius 200 km centred directly below theplatform. For elevations greater than 30 degrees the location must bewithin circle of radius 35 km centred below the platform. The latterconstraint is appropriate for communications between the ground and aplatform carrying only phased arrays situated in a horizontal plane. Theformer constraint may be appropriate for more complex array geometriesbut signal strength will become a limiting factor at distances over 100km which is discussed later.

Low installation cost: Use of platforms reduces the need for groundinstallations that are both time-consuming to install and expensive torun. Existing ground installations can be used in conjunction with thesystem to greatly increase capacity and coverage.

High data rate links: The traditional operation of a mobile networkdivides the network into a set of “cells.” Multiple UEs within a cellmust share the available resources (signal bandwidth and communicationpower), which determine the maximum data rate to a user either by radioresource sharing techniques, for example, but not exclusively, sharingbandwidth or time multiplexing. A key element is that inter-antennabeamforming is used to create a DF-Cell centred on a specific device.This permits all the resources, which can be made available by theimplemented protocol to be used by a single device. Resource sharing, asin standard implementations, is also supported by the invention.

Focused RF power at the user: Due to Inter-Antenna beamforming the powerat the precise user location is increased. This minimizes the powerusage on the platform and improves link quality. This is described indetail in Tables 2 and 3.

Scalable capability: The number of users and data rate can be increasedeasily and quickly—without normally the need for additional ground basedinfrastructure—by adding more platforms in the same area. The additionof extra BG stations can normally be avoided unless very large capacityincreases over the previous infrastructure is needed. This feature, initself, provides substantial resilience in the system. For example,losing one platform out of ten similar platforms, due to an equipmentfault or maintenance or temporarily being unavailable due to flightpatterns, would reduce the capacity of the system by 10%, but still givecomplete coverage within the service area. Similarly, losing one groundstation out of a hundred would also only lose 1% of the communicationdata rate capability. This is significantly better than the loss of astandard mobile phone cell mast where all users within the cells itcontrols will lose the signal.

Coverage area can be accurately tailored: Phased array and beamformingtechnology enables the coverage area to be more accurately controlledthan with ground-based systems. This is important for operation close tocountry borders.

For reliable communication, the beamforming technology needs to managethe effects of reflections such as from walls; or diffraction effectssuch as from the edges of intervening objects, such as the roofs ofbuildings, if the UE is ground based. Ideally the antennas on many ofthe platforms are in line-of-sight or close to it from the UE.

TABLE 3 Glossary of terms used in this document ADC Analogue to digitalconverter. Within the HAP-CELL systems converts the analogue RF signalto digital data stream for signal processing. Algorithm A process orcode by which the power levels at a particular UE can be set. This mightbe to optimise the powers to antenna elements to ensure a minimum powerlevel for all UE's or to ensure that given UE's had a higher powerlevel. Antenna A phased array or conventional antenna. Antenna elementAn individual transmitting or receiving antenna within a phased array.Each has an individual electronic system for linking to a signalprocessing system Antenna weightings or Typically, complex numbers thatare used within the signal processing chain to coefficients adjust theamplitude and phase of the signals to and from individual antennaelements to form the desired beams from an antenna or constellation ofantennas. Backhaul The data communication links from the aerialplatforms to the ground and communications ultimately to the HAP-CELLprocessing centre. Beam Directional signal transmission or receptionfrom an antenna Beamforming Beamforming is a signal processing techniqueused for multiple antennas or in the case of phased arrays, antennaelements, to give directional signal transmission or reception. This isachieved by combining the signals transmitted or received so that atparticular angles they experience constructive interference while othersexperience destructive interference. Beamwidth The angular beamwidth, asunderstood by practitioners skilled in the art, depends upon the ratioof the wavelength of the radiation used in said communications systemdivided by the separation between pairs of aerial antennas; for theconditions envisaged for this invention may be designed to be awavelength of 15 centimetres and an aerial antenna separation ofapproximately 10 kilometres results in a beamwidth of less than 50 microradians and beam size on the ground of less than 2 metres BeamformingTypically, these are complex numbers that are used within the signalprocessing coefficients chain to adjust the amplitude and phase of thesignals to and from individual antenna elements to form the desiredbeams from an array or constellation of arrays. BG stations Backhaulground stations. The ground based radio links to each of the platforms.Cell The logical functionality provided within an area on the earth'ssurface supplied with radio service. Each of these cells is assignedwith multiple frequencies. Constellation A number of antennas supportedby HAPs operating cooperatively over the same service area to providecommunications to many UEs. Conventional Antenna An antenna which is nota phased array Cooperative beam A highly directional signal transmissionor reception formed by coherently aligning beams from multiple antennasmounted on aerial platforms. Correlating Correlating is a mechanism tocross-multiply the signals to or from pairs of antenna elements, this isa fundamental part of interferometry to form the Fourier transform ofthe incoming or outgoing signals. DAC Digital to analogue converter.Within the HAP-CELL system converts a digital data stream into ananalogue RF signal for amplification and transmission via an antennaelement. DBF Digital beam-forming Femtocell The area, normally on theground, which is intersected by a beam carrying information to and froma piece of UE and at least three aerial antennas involved ininter-antenna cooperative beam forming. Dynamic femtocell (DF Afemtocell that is moved by changing antenna weights. Cell) Fleet Fleetof platforms supporting a constellation of antennas. HAP High AltitudePlatform. This is the vehicle that carries the communications equipment.It can e.g. be an unmanned aircraft, tethered balloon or untetheredballoon. HAP-CELL High altitude platform cellular system, which refersto an example of an implementation using HAPs to provide cellularcommunications. HAP-CELL Processing A facility associated with one ormore HAP-CELL systems to control the centre communications to and fromBG Stations, HAPs, UEs and the cellular network. Macrocells A cell in amobile phone network that provides radio coverage served by a high powercellular base station. MBDR Maximum Beam Data Rate from a single antennain a independent beam MBH Multiple beam horn (antennas) Microcell Amicrocell is a cell in a mobile phone network served by a low powercellular base station, covering a limited area such as a mall, a hotel,or a transportation hub. A microcell uses power control to limit theradius of its coverage area. Patch The patch is a specific area,normally on the ground, which can be illuminated by every antenna in theconstellation with an independent beam. Payload The equipment carried ona Platform. Phased Array A type of antenna consisting of many smallantenna elements, which are controlled electronically to form one ormore Phased Array Beams Phased arrays can be used on the HAPs or BGstations Phased Array Beam The electromagnetic beam formed by a phasedarray. Phased array beams from a HAP illuminates a patch. Platform Theplatform that carries the payload - an aircraft, tethered aerostat orfree flying aerostat. Service Area The area of ground over whichcommunications coverage is provided by one or more HAP-CELL aircraft. Aservice area is split into many patches. Spread Spectrum A technique inwhich a telecommunication signal is transmitted on a bandwidthTechnologies considerably larger than the frequency content of theoriginal information. Synthesised Beam The beam formed by beamformingHAPs in a constellation. The beam is small and illuminates a “dynamicfemtocell.” Transmitting data Data can be transmitted over an RF linksuch as the aerial antennas. Can also refer to communicating data withina system over local links such as fibres or wires. UE See UserEquipment. User Equipment The equipment used by an individual user,typically a mobile phone, tablet, or computer, but also more generallyequipment with or connected to an antenna which may be stationary or ina moving situation such as in a vehicle, vessel or aircraft. Abbreviatedto UE. User Beam A synthesised beam that tracks specific user equipmentWeightings See Antenna weightings

1. A process for cooperative aerial inter-antenna beamforming for communication between (a) multiple moving platforms, each platform having an aerial antenna mounted thereon, such that one or more of the aerial antennas have variable positions and orientations over time, and (b) at least one user antenna mounted on user equipment having a lower altitude than the aerial antennas; the process involving transmitting data relating to the positions and orientations of the aerial antennas to a processing system, the processing system calculating and transmitting beamforming instructions to the aerial antennas, the aerial antennas thereby transmitting or receiving respective component signals for each user antenna, the component signals for each user antenna having essentially the same information content but differing in their phase and usually amplitude, so as to form a cooperative beam from the cooperative sum of the signals between the aerial antennas and the user antenna.
 2. An apparatus for providing a communication network, for communication between (a) multiple moving platforms, each platform having an aerial antenna mounted thereon, such that one or more aerial antennas have variable positions and orientations over time, and (b) at least one user antenna mounted on user equipment having a lower altitude than the aerial antennas; the network involving a processing system adapted to receive data relating to the positions and orientations of the aerial antennas, the processing system being further adapted to generate and transmit beamforming instructions to the aerial antennas, the aerial antennas being adapted to generate or receive respective component signals for each user antenna, the component signals for each user antenna having essentially the same information content but differing in their phase and usually amplitude, so as to form a cooperative beam between the cooperative sum of the signals between the aerial antennas and the user antenna.
 3. The process according to claim 1, wherein there are at least three aerial antennas.
 4. The process according to claim 1, wherein the positional and orientation data is transmitted by the aerial antennas to at least one ground based station.
 5. The process according to claim 1, wherein the processing system comprises a ground based processing centre.
 6. The process according to claim 1, wherein the positions of the aerial antennas are known to within a quarter of a wavelength of the component signals.
 7. The process according to claim 1, wherein the aerial antennas define a notional antenna that has a dimension that is from 1 to 30 kilometres.
 8. The process according to claim 4, wherein ground level processing dominates the overall signal processing capability, consuming over 70 percent of the signal processing electronics power requirements.
 9. The process according to claim 1, wherein at least one aerial antenna is at an elevated location of at least 10,000 m.
 10. The process according to claim 1, wherein the cooperative beam is generated at a first point in time, and at a second point in time, carrying out a second beamforming operation to ensure that the cooperative beam is directed to the position of the moving user antenna.
 11. The process according to claim 10, wherein further beamforming operations are carried out over time to ensure that the cooperative beam is directed to the position of the moving user antenna.
 12. The process according to claim 1, wherein at least one of the aerial antennas are phased array antennas.
 13. The process according to claim 1, wherein at least one of the aerial antennas is connected to the ground.
 14. The process according to claim 1, wherein the platforms comprise unmanned solar powered aircraft, airships or hybrid air vehicles.
 15. The process according to claim 1, wherein the platforms comprise unmanned hydrogen powered aircraft.
 16. The process according to claim 1, wherein the platforms comprise tethered aerostats.
 17. The process according to claim 1, wherein the platforms comprise free-flying aerostats.
 18. The process according to claim 1, wherein the platforms comprise hydrocarbon-fuelled aircraft.
 19. The process according to claim 1, wherein the platforms comprise satellites.
 20. The process according to claim 1, wherein at least some of the platforms use different antennas for transmission or reception.
 21. The process according to claim 1, wherein the data rates to and/or from the user equipment antenna exceeds 10 Mbps.
 22. (canceled)
 23. The process according to claim 1, wherein the beamforming adapts to a changing position of user equipment to follow the user equipment to maintain high integrity communications.
 24. The process according to claim 1, wherein the beamforming is adapted dynamically by means of modifying aerial antenna weights to provide optimal service conditions.
 25. The process according to claim 1, wherein in which the user equipment is mobile.
 26. The process according to claim 1, wherein weightings of antenna elements are varied to control ground based patch sizes based on an optimization function reflecting population density or data rate density, taking into account the orientation and attitude of the antenna platform.
 27. The process according to claim 1, wherein at least some of the user equipment is ground based.
 28. The process according to claim 1, wherein at least some of the user equipment is on unmanned aerial vehicles.
 29. The process according to claim 1, wherein at least some of the user equipment is on manned aircraft.
 30. The process according to claim 1, wherein at least some of the user equipment is on some form of transportation technology.
 31. The process according to claim 1, wherein the aerial antennas are predominately carried by hydrogen powered aircraft in periods over a particular location when the solar illumination is low, and a solar and hydrogen powered aircraft in other periods.
 32. The process according to claim 1, implemented by multiple fleets of aerial platforms. 33-34. (canceled)
 35. A method of determining the position of a moving aerial antenna or antenna element mounted on at least one moving platform, such that the aerial antennas have variable positions and orientations over time, the method involving determining the phase difference y_(i), being a fraction of a wavelength between the values 0 and 1, between signals of known wavelength λ_(i) transmitted between (a) i ground based transmitters which may be backhaul base stations, wherein i is at least three, the ground based transmitters having known position to within λ_(i)/10 and (b) the aerial antenna or antenna element, thereby establishing the distance from the base station to the aerial antenna or antenna element to be λ_(i)(n_(i)+y_(i)), wherein n_(i) is an unknown integer; determining the position of the aerial antennas or antenna elements approximately by differential GPS or other methods to within a small number of wavelengths λ_(i) thereby establishing that n_(i) can be one of a limited number of possible integer values for each signal; the number of base stations and their positions being sufficient to allow elimination of the possible values of n_(i) that are inconsistent with the limited number of possible values for n_(i) from the other ground based transmitters, until only one integer value for each n_(i) is established; establishing the location of the aerial antenna or antenna element by triangulation of its known distance λ_(i)(n_(i)+y_(i)), from at least three ground based transmitters. 36-37. (canceled) 